Cyclonic fluid separator

ABSTRACT

A cyclonic fluid separator has a tubular housing ( 10 ) in which the fluid is accelerated and swirl imparting means ( 2 ) for inducing the fluid to swirl through an annular space between the housing and a central body ( 1 ) mounted within the housing ( 10 ), which central body ( 1 ) is provided with resonance abatement means, such as: tensioning means ( 20,22 ) which apply a tension load to an elongate tail section ( 8 ) of the central body ( 1 ) such that the natural frequency of the central body ( 1 ) is increased; vibration dampening means ( 31,50,60 ), which inhibit vibration of at least part ( 8 ) of the central body ( 1 ); solid particles ( 31 ) arranged in a segmented tubular tail section ( 8 ) of the central body ( 1 ), a viscous liquid ( 50 ) arranged between a tubular tail section ( 8 ) of the central body ( 1 ) and a tensioning rod ( 51 ), apertures ( 60 ) drilled radially through a tail section ( 8 ) of the central body ( 1 ); and/or a low pressure fluid ( 80 ) injected through a central opening ( 82 ) in the central body ( 1 ).

BACKGROUND OF THE INVENTION

The invention relates to a cyclonic fluid separator.

Gas mixtures may be separated by expanding and thereby cooling themixture such that condensable components condense and then separatingthe gaseous components from the condensed liquid components in acyclonic separator.

International patent application WO03029739 discloses a cyclonicseparator comprising a throat section in which the fluid may beaccelerated to a transonic or supersonic velocity and swirl impartingmeans for inducing the fluid to swirl through an annular space betweenthe housing and a central body, which is arranged substantiallyco-axially relative to a central axis of the housing.

The fluid mixture that flows at high velocity through the annular spacebetween the inner surface of the housing and the outer surface of thecentral body may exert vibrating forces on the housing and the centralbody.

It is also desired to streamline the central body, which may involveconfiguring the central body such that is has a droplet shaped frontsection and an elongate slender tail section. This tail section may beshort or long and may be supported or unsupported by the housing.Vibrations of the central body may have a detrimental effect on thefluid flux and separation performance of the device and may damage andeven cause failure of the central body.

It is an object of the present invention to solve the problem ofvibration of the central body of a cyclonic fluid separator.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a cyclonic fluidseparator with a tubular housing in which the fluid is accelerated andswirl imparting means for inducing the fluid to swirl through an annularspace between the housing and a central body mounted within the housing,which central body is provided with resonance abatement means.

Optionally the resonance abatement means are configured to increase thenatural frequency of the central body and/or to dampen vibrations of atleast part of the central body.

To achieve this the central body may comprise a tubular tail section,which is at least partially filled with solid particles and/or a viscousliquid and which may be subject to a predetermined axial tension.

Furthermore, a tension rod may be arranged in the tubular tail sectionof the central body, such that an annular gap is present between theouter surface of the tension rod and the inner surface of the tubulartail section of the central body, which annular gap is at leastpartially filled with a viscous liquid.

Alternatively, the central body may comprise a porous tail section, suchthat pressure differences between opposite sides of the tail section arereduced and vibration of the tail section resulting from any varyingpressure differences between said opposite sides of the tail section isinhibited.

In such case the central body may have a droplet shaped front sectionand an elongated substantially cylindrical tail section which is madesubstantially porous by perforating the tail section by substantiallyradial holes that are distributed along the length of the tail section,which holes are also distributed at regular tangential intervals alongthe circumference of the tail section.

In another embodiment of the cyclonic fluid separator according to theinvention the central body comprises a longitudinal opening having alongitudinal axis which substantially coincides with the central axis,which longitudinal opening is configured as a duct through which in usea low pressure fluid is injected into the tubular housing, which lowpressure fluid is mixed with the fluid flowing through the throatsection in a substantially cylindrical section of the housing that islocated downstream of the throat section and which low pressure fluidhas a lower static pressure than the fluid flowing via the throatsection into the substantially cylindrical section of the housing.

In such case the tubular housing may comprise a tail section in which acentral gas enriched fluid outlet is arranged, which is surrounded by anannular liquid enriched fluid outlet and wherein a recycle conduit isarranged between the annular liquid enriched fluid outlet and thelongitudinal opening in the central body for recycling liquid enrichedfluid as a low pressure fluid from the annular liquid enriched fluidoutlet into the longitudinal opening in the central body.

The throat section of the cyclonic fluid separator according to theinvention may be configured such that in use the fluid accelerated to asubstantially sonic or supersonic velocity in the throat section andthereby cooled such that one or more condensable components condense inthe throat section.

In accordance with the invention there is also provided a method ofseparating a fluid mixture with the separator according to theinvention, wherein the method is used to obtain a purified natural gasstream from a contaminated natural gas stream comprising solidcontaminants, such as sand and/or other soil particles and/orcondensable contaminants, such as water, condensates, carbon dioxide,hydrogen sulphide and/or mercury.

These and other features, objects, advantages and embodiments of thecyclonic separator and method according to the invention are describedin the accompanying claims, abstract and following detailed descriptionof preferred embodiments in which reference is made to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic longitudinal sectional view of a cyclonicseparator with a central body having an elongate tail section;

FIG. 2 depicts at a larger scale a schematic three-dimensional view ofthe clamp construction, which applies a tension load to the downstreamend of the tail section of the central body shown in FIG. 1;

FIG. 3 is a cross-sectional view of a segmented tubular tail section ofthe central body shown in FIG. 1, which is filled with solid particles;

FIG. 4 is a longitudinal sectional view of the segmented tubular tailsection shown in FIG. 3;

FIG. 5 is a cross-sectional view of tubular tail section of the centralbody shown in FIG. 1, which is filled with a viscous liquid and arrangedaround a tensioning rod;

FIG. 6 is a cross-sectional view of a perforated elongated tail sectionof the central body shown in FIG. 1;

FIG. 7 is a longitudinal sectional view of the perforated elongated tailsection shown in FIG. 6; and

FIG. 8 is a schematic longitudinal sectional view of a cyclonic fluidseparator with a central body having a central opening through which alow-pressure fluid is injected to inhibit fluid induced vibrations.

DETAILED DESCRIPTION OF DEPICTED EMBODIMENTS

In the accompanying FIGS. 1-8 similar reference numerals are used, whereappropriate, to denote similar components of similar embodiments of thecyclonic fluid separators depicted therein.

Referring now to FIG. 1, there is shown a cyclonic inertia separatorwhich comprises a swirl inlet device comprising a streamlineddroplet-shaped central body 1 on which a series of swirl imparting vanes2 are mounted and which is arranged co-axial to a central axis I of theseparator and inside the separator housing 10 such that an annular flowpath 3 is created between the central body 1 and separator housing 10.The separator further comprises an annular throat portion 4 from whichin use the swirling fluid stream is discharged into a diverging fluidseparation chamber 5 which is equipped with a central primary outletconduit 7 for gaseous components and with an outer secondary outletconduit 6 for condensables enriched fluid components. The central body 1has a substantially cylindrical elongated tail section 8 on which anassembly of flow straightening blades 9 is mounted. The central body 1preferably has a largest outer width or diameter 2 R_(o max), which islarger than the smallest inner width or diameter 2 R_(n min) of theannular throat portion 4.

The swirl imparting vanes 2 are oriented at an angle (α) relative to thecentral axis I to create a circulation (Γ) in the fluid stream. It ispreferred that α is between 20° and 50°. The fluid stream issubsequently induced to flow into the annular flow area 3. Thecross-sectional surface of this area is defined as:A_(annulus)=π·(R_(outer) ²−R_(inner) ²).

The latter two being the outer radius and inner radius of the annulus ata selected location.

The mean radius of the annulus at that location is defined as:R _(mean)=√[½(R _(outer) ² +R _(inner) ²)]

At the maximum value of the mean annulus radius R_(mean,max) the fluidstream is flowing between the assembly of swirl imparting vanes 2 at avelocity (U), which vanes deflect the flow direction of the fluid streamproportional to the deflection angle (α) and so obtaining a tangentialvelocity component which equals U_(φ)=U·sin(α) and an axial velocitycomponent U_(x)=U·cos(α).

In the annular space 3 downstream of the swirl imparting vanes 2 theswirling fluid stream is expanded to high velocities, wherein the meanannulus radius is gradually decreasing from R_(mean),max toR_(mean,min).

It has been found that during this annular expansion two processesoccur:

(1) The heat or enthalpy in the flow (h) decreases with the amountΔh=−½U², thereby condensing those flow constituents which first reachingphase equilibrium.

This results in a swirling mist flow containing small liquid or solidparticles.

The tangential velocity component increases inversely with the meanannulus radius Uφ substantially in accordance with the equation:U _(φ,final) =U _(φ,intial)·(R _(mean,max) /R _(mean,min))

This results in a strong increase of the centrifugal acceleration of thefluid particles (a_(c)), which will finally be in the order of:a _(c)=(U _(φ,final) ² /R _(mean,min)).

In the tubular throat portion 4 the fluid stream may be induced tofurther expand to higher velocity or be kept at a substantially constantspeed. In the first case condensation is ongoing and particles will gainmass. In the latter case condensation is about to stop after a definedrelaxation time. In both cases the centrifugal action causes theparticles to drift to the outer circumference of the flow area adjacentto the inner wall of the separator housing, which is called theseparation area. The time period for the particles to drift to thisouter circumference of the flow area determines the length of thetubular throat portion 4.

Downstream of the tubular throat portion 4 the condensables enriched‘wet’ fluid components tend to concentrate adjacent to the inner surfaceof the diverging fluid separation chamber 5 and the ‘dry’ gaseous fluidcomponents are concentrated at or near the central axis I, whereupon thewet condensables enriched ‘wet’ fluid components discharged into anouter wet fluid outlet 6 via one slot or a series of slots, (micro)porous portions whereas the ‘dry’ gaseous components are discharged intothe central dry fluid outlet conduit 7.

In the diverging central dry fluid outlet conduit 7 the fluid stream isfurther decelerated so that the remaining kinetic energy is transformedinto potential energy. The diverging central dry fluid outlet conduit 7can be equipped with an assembly of flow straightening vanes 9 torecover the circulation energy.

The gas mixture enters the separator shown in FIG. 1 at the left. Thegas is guided over the central body 1 through a narrow, ring-shaped flowduct, whilst gaining angular momentum induced by the guiding vanes 2placed around the perimeter of the central body 1. The swirling flow isexpanded along the annular duct 4. The swirl gains strength whileexpanding in the contraction towards section 4. During the expansion,the high boiling gas components will start to condense between the swirlimparting vanes 2 and the throat section 4 while the lower boilingcomponents will start to condense between the throat section 4 and thevortex finder of the fluid separation chamber 5. The resulting dropletsare transported to the outer perimeter of the flow area due to theimposed centrifugal forces of the swirling motion. At the vortex finder5 the flow is split into a wet stream at the outer perimeter of theflow, and a dry stream in the core of the flow.

By extending the central body 1 with an elongated tail section 8, thesteep increase of tangential momentum towards the central axis of thevortex flow, is restricted thereby avoiding flow instability (i.e.vortex break down). The presence of the centrally placed droplet-shapedcentral body 1 with elongated tail section 8 is beneficial to provide asupersonic cyclonic separator with high separation efficiency. Highseparation efficiency is obtained through maximizing the angularmomentum in the flow. However increasing the angular momentum is limitedby the occurrence of vortex breakdown. The latter strongly diminishesthe angular momentum. The droplet shaped central body 1 allows for anincrease of angular momentum in the cross section flow—compared to aflow area without central body—without the occurrence of vortexbreakdown. Alternatively said restriction provided by the elongated tailend section can be obtained by injecting a low pressure fluid through alongitudinal opening at the end of the droplet shaped central body asshown in FIG. 8.

Considering a central body 1 comprising an elongated tail end section 8,centrally placed in a cylindrical flow duct in which a flow isestablished. An infinitesimal small displacement from an initial radialposition r=(x₀, y₀) to a new radial position r=(x₁, y₁), will cause theflow to accelerate in the part of the flow cross-section where thecentral body has been displaced to, and decelerate in the part of theflow cross section from which the central body 1 was displaced. Clearlythe resulting static pressure difference will generate a lift force,which by definition is normal to the surface of the central body 1. Thisnormal force will cause further bending, leading to a new radialposition r=(x₂, y₂) etc. etc. The magnitude of the final displacement isa result of the flow force (i.e. normal force) on one hand, counteractedby the bending stiffness of the central body 1 (i.e. reaction force perunit displacement) on the other hand. If the bending stiffness of thecentral body 1 is sufficiently high, the resultant force has a directionopposite to the direction of displacement, for which holds that thecentral body structure behaves as a mass-spring system. If however thebending stiffness is insufficient the resultant force is in thedirection of the displacement and the central body 1 will be displacedtowards the boundary of the housing 10 or until material rupture due toa load beyond the ultimate strength limit. The bending stiffness willmerely depend on: Moments of Inertia (i.e. central body shape), Modulusof Elasticity of the material (E) and the Pretension Force imposed onthe central body 1.

Forces exerted by the swirling fluid flux on the central body 1 can becalculated as follows.

Considering a central body 1 centrally placed in a cylindrical flow ductbut now with a vortex flow present. An infinitesimal small displacementfrom an initial radial and tangential position [r, φ]=(x₀, y₀) to a newposition [r, φ]=[x₁, y₁], will not only cause a force normal to thecentral body surface, but also a force tangent to the central bodysurface which causes a disposition in tangential direction. Thistangential movement of the central body is not restraint by its bendingstiffness—which only works in radial direction—hence an ongoing pivotingmovement of the central body results. To avoid an increasing pivotingmotion, a dampening mechanism is required to stabilize the central body.

Summarizing the above, a static stable central body 1 behaves like amass-spring system hence will oscillate in a harmonic mode at itsnatural frequency as long as the flow is exciting the central body 1.The corresponding amount of free resonance energy needs to be removedfrom the system (i.e. needs to be dissipated). Therefore a dampeningmechanism is required to obtain dynamic stability. Alternatively themass-stiffness of the central body structure can be increased to thepoint that its natural frequency becomes so high that the period of theoscillation is small compared to the retention time of gas flow. In thatcase the flow will not exert a defined lift force on the central body 1,hence is not excited. In addition the lift forces on the central body 1can be suppressed by radially oriented openings throughout the centralbody cross section balancing the pressure between lower and upper side.

Suitable ways to support the droplet shaped central body 1 with anelongate tail section 8 such that vibrations are inhibited are describedherein below.

In the embodiment shown in FIG. 1 the swirl imparting vanes 2 and thede-swirling vanes 9 support the central body 1 with an elongated tailsection 8 within the tubular separator housing 10. Since the swirlimparting vanes 2 and de-swirling vanes 9 protrude into the fluid flow,it is preferred to place these in the low speed areas of the flow (<200m/s) as to avoid unnecessary pressure loss. The triangles 11,12, and 13show how in the supersonic cyclonic separator shown in FIG. 1 thedroplet shaped central body 1 with elongated tail section 8 may besupported within the tubular separator housing 10:

-   1) a fixed support 11 is provided by the swirl imparting vanes 2,-   2) a radial restraint support 12 is provided by spacer ribs 14 in    the dry gas outlet conduit 7, and-   3) a fixed support 13 in the dry gas outlet conduit 7 downstream of    the de-swirling vanes (9).

By choosing the support types and support locations for a given centralbody geometry, its mode shape is determined as well as its moments ofinertia. The number of support points can be any number larger than orequal to 2 depending on the specific geometry of the supersonic cyclonicseparator.

By applying a pretension load on the central body 1 with elongate tailsection 8 the bending stiffness increases i.e. the static stabilityincreases and therefore its natural frequency increases. It willunderstood that increasing the natural frequency of the central bodywill also enhance the actual dampening. Since the pretension load can goup to an average tensile stress of 5000 MPa in the cross section of thetail section 8 of the central body 1. In the case of a high pretensionload>1000 MPa, it is preferred to avoid thread connections.

Therefore a special clamp construction as shown in FIG. 2 may be used tohold the downstream end, and optionally also the upstream end, of thecentral body 1, 8 in position, and taking up the tensile load.

The downstream end of the tail section 8 of the central body 1 isclamped in a conical tube 20 in which longitudinal grooves 21 can be cutto provide conical wedges 20A, 20B. This wedged conical tube 20 istightly squeezed between the outer surface of the tail section 8 of thecentral body 1 and the inner surface of the clamp housing 22, as soon asan axial load is applied on the central body 1.

Suitable materials for constructing a central body 1 with an elongatedtail section 8 are:

-   -   materials with a high modulus of elasticity, or E-modulus, in        order obtain sufficient material stiffness,    -   materials with a high yield strength in order to enable high        tension load to increase stiffness,    -   impact load in order to warrant operational robustness; and    -   materials with a high resistance against corrosion and hydrogen        embrittlement to avoid hydrogen induced cracking, within an low        temperature range, typically from 0° C. down to −100° C.

Two types of materials comply with these requirements:

-   1) high grade hardened steel alloys and,-   2) unidirectional carbon fibre reinforced resins.

Suitable high grade hardened steel alloys (1) are cold worked alloyscontaining at least the following components: Chromium, Nickel,Molybdenum and Cobalt.

Suitable unidirectional carbon fibre reinforced resins (2) comprise HighModulus carbon fibres with a filling percentage of at least 40 vol %.Optionally filling the voids between the fibres with nano tubes canfurther reinforce the fibre matrix.

A resonance dampener may be used to dissipate the vibration energyextracted from the flow, in order to avoid dynamic instability (i.e.increase of deflection/displacement). The oscillation mode is determinedby the first mode shape of the central body 1 with elongate tail section8 and the distances between the support points 11,12 and 13.

The higher the bending stiffness and the lower the specific mass of thecentral body 1 with elongate tail section 8, the higher its naturalfrequency. For a given level of excitation power—exerted on the centralbody—a higher natural frequency yields a smaller deflection of thecentral body. The lower limit of the maximum allowable deflection isdetermined by the flow disturbance caused by the deflection andtypically ranges between 1% and 5% of the smallest diameter of thecentral body. The upper limit of the maximum allowabledeflection—typically ranging from 5% to 50% of the smallest diameter ofthe central body—is determined by the yield strength of the material andthe moment of inertia of the central body shape, since an increase ofdeflection causes an increase in stress in the central body in theproximity of the support points. In general it can be stated that thehigher the bending stiffness the higher the stress level per unitdeflection, hence the lower the upper limit of allowable deflection.However, this is compensated because the higher the bending stiffnessthe higher the natural frequency and the smaller the actual deflection.

FIG. 3-5 illustrate two concepts, which diminish the resonance levels inthe central body 1 with elongated tail section 8 shown in FIG. 1 withinthe limits of maximum deflection:

-   1) Particle dampener shown in FIGS. 3 and 4, and-   2) Viscous liquid dampener shown in FIG. 5.

The particle dampener shown in FIGS. 3 and 4 comprises one or morecylindrical cavities 30 inside the tail section 8 of the central body 1,which cavities 30 are at least partly filled with small particles 31.The principle of the particle dampener is that the majority of theparticle mass is brought into a movement due to the vibration of thetail section 8 of the central body 1 induced by the flow forces. Themajority of the particle mass should make an oscillatory movement out ofphase with the oscillation of the tail section 8 of the central body 1itself. The oscillation energy of the tail section 8 is then dissipatedthrough collision between particles and the wall of the tail section 8of the central body 1 and collisions between particles mutually.

The filling or packing rate should be at least 60% (excluding the porevolume between the particles which is typically 25-30% vol. %) with amaximum filling rate of 95%. The preferred filling rate is between 75and 85%. The particles 31 may have diameters d that may vary between 0.1and 5 mm and that preferably are between 0.6 and 2.2 mm. However abetter measure is ratio d/D1 of the particle diameter d divided by theinternal diameter D1 of the tail section 8, which may vary between 0.04and 0.25. The ratio d/D1 is preferably selected in the range of 0.12 and0.2. The mass density of the particle material is chosen high, at leastabove 3 kg/m³, preferably above 8 kg/m³. The material of the particles31 should be extremely wear resistant. A suitable material for theparticles 31 is Tungsten Carbide (WC). The voids between the particles31 can be filled with air or another suitable gas. It is also possibleto use a liquid for this purpose provided the viscosity is not extremelyhigh.

The preferred dimensions of the cylindrical cavity 30 in the tailsection 8 are between D1 _(min)=0.4*D2 and D1 _(max)=0.8*D2.

It is furthermore preferred to apply a segmentation in longitudinaldirection of the tail section 8 as to avoid particles 31 to concentratein one of the outer ends of the cylindrical cavity 30 i.e. to ensure theparticle distribution is as uniform as possible over the length scale ofthe tail section 8 of the central body 1.

FIG. 5 shows a tail section 8 comprising a series of cavities 30A-30D,which are filled with particles 31 and which are separated by separationdisks 32A-32D. The preferred length scale of each cavity segment 30A-30Dis between L1=1*D1 and L1=4*D1. The preferred filling rate is =75-85 vol% of particles 30 per segment 30A-30D.

FIG. 5 shows a tail section 8 of a central body 1, which is equippedwith a liquid dampener. The liquid dampener is arranged in a tubulartail section 8 of the central body 1, which is filled with a viscousliquid 50 and in which a tension rod 51 is arranged. The annular gapbetween the outer diameter of the tension rod and the inner diameter ofthe tubular tail section 8 of the central body 1 is filled with aviscous fluid 50.

The tension rod 51 is put under a high tensile force, yielding anaverage tensile stress between 1000-5000 MPa. The tail section 8 of thecentral body 1 is mounted either without pretension or with a slightlyelevated pretension, yielding an average tensile stress between 0-500MPa. Because the natural frequency of the tension rod 51 is much higherthan the natural frequency of the tubular tail section 8 of the centralbody 1 itself, relative movement between the rod 51 and the tail section8 exists if the tail section 8 is excited. As a result the viscous fluid50 present in the gap between the rod 51 and the tail section 8 isdisplaced in an alternating mode. In this way the resonance energy,gained by the elongate tail section 8 of the central body 1, isdissipated by viscous forces in the alternating moving fluid 50. Theviscous fluid 50 can be any vapour, liquid, liquid-liquid emulsion orsolid-liquid suspension with a dynamic viscosity between 10⁻⁴ and 10⁻²Pa·s in a temperature range between 240-270 K. Preferably the viscousfluid is non-corrosive and preferably its viscosity is only weaklydepending on temperature. A suitable viscous fluid is a non-Newtonianfluid. For instance a shear-thinning fluid may be applied in order tomaximize the dampening in the small amplitude range i.e. when therelative movement between the rod and the central body is small.

The material of the tail section 8 of the central body 1 can be anysuitable corrosion resistant alloy (e.g. AISI316, Inconel, Incolloy,MP35N, etc) or a fibre reinforced material (resin/alloy). The tensionrod 51 may be made of a material with a high tensile strength such asMP35N, Maraging or a carbon fibre reinforced epoxy matrix.

The preferred dimensions of the annular gap between of the inner surfaceof the tubular tail section 8 having an inner diameter D1 and an outerdiameter D2 and a tension rod having an outer diameter D3 are asfollows:D1_(min)=0.60*D2:D1_(max)=0.95*D2D3_(min)=0.70*D1:D3_(max)=0.95*D1

FIGS. 6 and 7 show an embodiment of the elongated tail section 8,wherein the tail section is perforated by radial apertures 60 in orderto create a substantially porous tail section 8. The apertures 60 serveto inhibit radial forces exerted by the swirling fluid flow 61 aroundthe tail section 8. In order to avoid destabilization of the tailsection 8 of the central body 1, which is exposed to normal forcesexerted by the swirling vortex flow 61, the surface of the tail section8 of the central body 1 is partially porous, allowing for equalizationof pressure perturbations around the elongated tail section 8 of thecentral body 1.

When considering an elongated cylindrical tail section 8 surrounded by aconfined vortex flow 61, a deflection of the tail section 8 in radialdirection would normally create a normal force acting in the samedirection as the deflection. This normal force results from a low staticpressure P_(low) in the swirling fluid flow 61 at an upper surface ofthe tail section 8, while at the opposite lower surface of the tailsection 8 a high pressure P_(high) exists. The apertures 60 serve toequalize this pressure differential Δ(P_(high)−P_(low)) by connectingopposite sides of the tail section 8 by means of diametrically drilledapertures.

FIG. 6 illustrates and embodiment wherein three apertures 60A-C aredrilled at regular tangential intervals of 60 degrees through one crosssectional surface of the tail section 8 to inhibit pressure differencesbetween the fluid flux at different sides of the tail section 8.

Typically the number (n) of apertures 60 per cross section of the tailsection 8 may vary from a minimum of 2 up to 40 depending on thecharacteristic size of the of the aperture 60. The smaller the ratiod/D1 between the diameter of the aperture 60 and the diameter of thetail section 8 the larger n can be. It is preferred to restrict theminimum value of d/D1≧0.03 and the maximum value of d/D1≦0.3. Theminimum value of d/D1 is determined by the risk of plugging the holeswith debris or ice/hydrates which increase if d becomes smaller, whilethe maximum is governed by the disturbance of the surface discontinuityon the vortex flow which becomes larger when d increases. Once the ratiod/D1 is chosen the suppression of the normal flow forces is determinedwith the total number of holes (N) which follows from the number ofholes per cross section (n) times the number of perforated crosssections along the length scale (i). The total surface porosity definedas P=n*(d²/D1)*(i/L) can range between 0.1≦P≦0.8 though it is preferablybetween 0.3 and 0.6.

FIG. 8 shows an embodiment of the cyclonic separator according to theinvention wherein the functionality of elongated tail section 8 of theseparators shown in FIG. 1-7 is replaced by injecting a low pressurefluid 80 through a central opening 82 of the central body 1 into thecore of the vortex 81 flowing through the tubular housing 10 of theseparator. A swirling motion can be imposed to the low pressure fluidprior to injection via the central opening 82. This swirling motion canbe either co-current or counter-current to the swirling motion of thehigh pressure flow.

The entrance momentum of the low pressure fluid 80 will be low comparedto the momentum of the high pressure flow 81 passing along the outersurface of the central body 1. Extensive momentum exchange will occur inthe elongate tubular fluid separation section 4 of the device where thelow pressure fluid 80 is propelled by the high pressure swirling fluid81. Likewise the central body 1, tangential momentum in the highpressure swirling fluid 81 is limited by the presence of a low momentumflow in the core of the tube section 4. As the swirling high pressurefluid flux 81 will loose tangential momentum, the low pressure fluidflux 80 will gain tangential momentum. The low pressure fluid flux 80 intotal will mix with the swirling high pressure fluid flux 81 andaccelerated in the tubular separation section 4.

The liquids formed by nucleation and condensation will be offeredsufficient retention time in the tubular separation section 4 that theseare separated in the vortex flow to the outer perifery of the tube.

The low pressure fluid may be a fraction of the liquid enriched ‘wet’fluid flowing from the annular wet gas exhaust conduit 6, which isrecirculated into the opening 82 within the central body 1 via wet gasrecycling conduit 84. The wet gas recycling conduit 84 is equipped witha control valve 85 to control the low pressure fluid flow rate 80 suchthat is between 5 and 80% of the fluid flow rate of the high pressurefluid 81. It is preferred that the low pressure fluid flow rate 80 isbetween 25 and 60% of the high pressure fluid flow rate.

1. A cyclonic fluid separator with a tubular housing (10) in which thefluid is accelerated and swirl imparting means (2) for inducing thefluid to swirl through an annular space between the housing and acentral body (1) mounted within the housing (10), characterized in thatthe central body (1) is provided with resonance abatement means, whereinthe resonance abatement means comprise: tensioning means (20,22) whichapply a tension load to an elongate tail section (8) of the central body(I) such that the natural frequency of the central body (1) isincreased, wherein the tensioning means (20, 22) comprise a clampconstruction to hold the downstream end of the central body (1) inposition, the clamp construction comprising a conical tube (20) and aclamp housing (22), wherein the conical tube (20) is tightly squeezedbetween the outer surface of the tail section (8) of the central body(1) and the inner surface of the clamp housing (22).
 2. The cyclonicfluid separator according to claim 1, wherein the central body (1)comprises a tubular tail section, which is at least partially filledwith solid particles and/or a viscous liquid, wherein the viscous liquidis a vapour, liquid, liquid-liquid emulsion or solid-liquid suspensionwith a dynamic viscosity between 10⁻⁴ and 10⁻² Pa·s in a temperaturerange between 240-270 K.
 3. The cyclonic fluid separator of claim 1,wherein the central body (1) comprises a droplet shaped section, whichhas a longitudinal axis of symmetry which is substantially co-axial to acentral axis of the tubular housing, such that an annular fluid channel(3) is created between the outer surface of the central body (1) and theinner surface of the tubular housing, in which annular fluid channel (3)a series of swirl imparting vanes (2) are arranged, which swirlimparting vanes (2) are arranged around a large diameter mid section ofthe droplet shaped section and which annular fluid channel (3) providesa throat section (4) which is arranged around a section of the centralbody (1) having a smaller outer diameter than the mid section of thecentral body (1).
 4. The cyclonic fluid separator of claim 1, whereinthe throat section is configured such that in use the fluid acceleratedto a substantially sonic or supersonic velocity in the throat section(4) and thereby cooled such that one or more condensable componentscondense in the throat section.
 5. The cyclonic fluid separator of claim1, wherein the resonance abatement means further comprise one or more ofthe following vibration dampening means, which inhibit vibration of atleast part of the central body (1) solid particles (31) arranged in asegmented tubular tail section (8) of the central body (1); a viscousliquid (50) arranged between a tubular tail section (8) of the centralbody (1) and a tensioning rod (51); apertures (60) drilled radiallythrough a tail section (8) of the central body (1).
 6. Cyclonic fluidseparator according to claim 1, wherein a pretension load is applied onthe central body, wherein the pretension load >1000 MPa.
 7. Cyclonicfluid separator according to claim 1, wherein the conical tube (20)comprises longitudinal grooves (21) providing conical wedges (20A, 20B).8. The cyclonic fluid separator of claim 1, wherein the resonanceabatement means comprise vibration dampening means, which inhibitvibration of at least part of the central body (1).
 9. The cyclonicfluid separator of claim 8, wherein a tension rod (51) is arranged inthe tubular tail section of the central body (1), such that an annulargap is present between the outer surface of the tension rod (51) and theinner surface of the tubular tail section of the central body (1), whichannular gap is at least partially filled with a viscous liquid.
 10. Thecyclonic fluid separator of claim 8, wherein the viscous liquid is ashear-thinning non-Newtonian fluid.
 11. The cyclonic fluid separator ofclaim 8, wherein the central body (1) comprises a porous tail section,such that pressure differences between opposite sides of the tailsection are reduced and vibration of the tail section resulting from anyvarying pressure differences between said opposite sides of the tailsection is inhibited.
 12. The cyclonic fluid separator of claim 11,wherein the tail section of the central body (1) extends through atleast a substantial part of the length of the tubular housing and isprovided with holes that have a substantially radial orientationrelative to a longitudinal axis of the tail section (8), and which holesprovide fluid communication between opposite sides of the tail section(8) of the central body (1).
 13. The cyclonic fluid separator of claim12, wherein the central body (1) has a droplet shaped front section andan elongate substantially cylindrical tail section (8) which is madesubstantially porous by perforating the tail section (8) bysubstantially radial holes that are distributed along the length of thetail section (8), which holes are also distributed at regular tangentialintervals along the circumference of the tail section (8).
 14. A methodof separating a fluid mixture, comprising: providing a cyclonic fluidseparator with a tubular housing (10) in which the fluid is acceleratedand swirl imparting means (2) for inducing the fluid to swirl through anannular space between the housing and a central body (1) mounted withinthe housing (10), characterized in that the central body (1) is providedwith resonance abatement means, wherein the resonance abatement meanscomprise tensioning means (20,22) which apply a tension load to anelongate tail section (8) of the central body (I) such that the naturalfrequency of the central body (1) is increased, wherein the tensioningmeans (20, 22) comprise a clamp construction to hold the downstream endof the central body (1) in position, the clamp construction comprising aconical tube (20) and a clamp housing (22), wherein the conical tube(20) is tightly squeezed between the outer surface of the tail section(8) of the central body (1) and the inner surface of the clamp housing(22); and using the cyclonic fluid separator to obtain a purifiednatural gas stream from a contaminated natural gas stream comprisingsolid contaminants and/or condensable contaminants.
 15. The method ofclaim 14, wherein the cyclonic fluid separator further comprisesresonance abatement means comprising one or more of the followingvibration dampening means, which inhibit vibration of at least part ofthe central body(1) solid particles (31) arranged in a segmented tubulartail section (8) of the central body (1); a viscous liquid (50) arrangedbetween a tubular tail section (8) of the central body (1) and atensioning rod (51); apertures (60) drilled radially through a tailsection (8) of the central body (1).
 16. The method of claim 14, whereinthe solid contaminants are sand and/or soil particles, and thecondensable contaminants are water, condensates, carbon dioxide,hydrogen sulphide and/or mercury.